Not sure I would trust poly for other than towing a lightweight dingy.
The standards to which it is made would need some investigation in my mind. I have seen large diameter poly used in some commercial applicstions...but it is always new and probably checked regularly. I think the local clamp boats use it on their hydraulic dredges, and that is definitely a pull test.
But......
I watched a tug of war between cub scouts, 50 or so on a team, part poly that was 4 inches or so in diameter. I melted through at the parting point...looked like it had been cut by a hot knife.
A factory flaw maybe? As I have a hard time believing there was that much pull on it as kids were sliding, slipping, falling, etc all along each side....
Thus my distrust in even checking a small porion as it may have a flaw in the middle...